Symbol¶

The symbol statement defines the mapping between a component's ports and the pins of a schematic symbol.

A pcb-component can have one or more schematic symbols associated with it. For the case where multiple schematic symbols are associated with a component, we consider each distinct schematic symbol a "Unit". For the single schematic symbol the "unit" connotation is implied.

Signature¶

  ; Single Symbol Unit Declaration
  symbol = <SYMB>( <PORT-1> => <SYMB>.<PIN-1>, <PORT-2> => <SYMB>.<PIN-2>, ... )

  ; Multi-Symbol Unit Declaration
  symbol : 
    unit(<BANK-ID>) = <SYMB>( 
      <PORT-1> => <SYMB>.<PIN-1>, 
      <PORT-2> => <SYMB>.<PIN-2>, 
      ... 
      )
    ...

  ; With a Pin Property Table
  assign-symbol(<SYMB>)

  assign-symbols([
    <BANK-ID> => <SYMB-1>,
    <BANK-ID> => <SYMB-2>,
    ...
  ])

symbol = - This is an explicit mapping statement for a single schematic symbol unit. Notice that there is no <BANK-ID> in this declaration as the unit is implied.
<SYMB> - This is a pcb-symbol definition.
<PORT-1> - This is a port on the current pcb-component definition by ref.
<PIN-1> - This is a pin of the <SYMB> definition. Note that we use dot notation to access this pin definition.
=> is a mapping operator
symbol: - This is a method of providing multiple schematic symbol units for this component definition via explicit mapping.
The <BANK-ID> is typically of type Int|Ref. It is used to uniquely identify a particular schematic symbol unit.
- In Altium - you would like see a fixed sub-symbol identifier as A, B, etc.
- In JITX - you can identify units as a number 0, 1, etc or as a Ref symbol such as power, config, etc
Notice that for each unit() statement we use the same mapping syntax as for the single unit case.
assign-symbol() - This is a utility function for constructing the mapping when the user has defined a pin-properties table.
The <SYMB> argument is a pcb-symbol definition.
assign-symbols() - Similar to assign-symbol but this handles the multiple symbol unit case.
This function expects a tuple of mappings between the <BANK-ID> and the <SYMB>

Usage¶

There are two primary ways to utilize the symbol statement:

Explicit Mapping
Pin Properties Table Mapping

Explicit Mapping¶

pcb-component op-amp :
  port supply : power
  port vin : diff-pair
  port vout : pin

  symbol = op-amp-sym(
    self.vin.P       => op-amp-sym.vin.P
    self.vin.N       => op-amp-sym.vin.N
    self.vout        => op-amp-sym.out
    self.supply.vdd  => op-amp-sym.v+
    self.supply.gnd  => op-amp-sym.v-
  )


pcb-symbol op-amp-sym :
  pin v- at Point(0.0, -2.0)
  pin v+ at Point(0.0, 2.0)
  pin vin.N at Point(-2.0, -1.0)
  pin vin.P at Point(-2.0, 1.0)
  pin out at Point(2.0, 0.0)

  ; More Symbol Geometry Here
  ...

In this example, we define the ports of the op-amp component as bundles and single pin ports. These ports don't match 1:1 with the symbol's pin declarations. This is an example of a case where an explicit symbol mapping statement is required.

The mapping statements self.vin.P => op-amp-sym.in+ are on single pins only. There is no way to map bundle to bundle between component port and symbol pins. If you were to try and do something like:

  symbol = op-amp-sym(
    self.vin       => op-amp-sym.vin
    ...
  )

You would see an exception like this:

Uncaught Exception: ... : Must map to a symbol pin with a single pin (received a pin bundle).

Further - this mapping function has the following expectations:

Each component port must have a mapping
1. If you were to forget a port in the mappings, this would elicit a Uncaught Exception: ... : Every component pin must have an entry in a symbol mapping. error.
Each port to symbol mapping must be unique.
1. If you were to make two mappings that both referenced self.vout, this would elicit a Uncaught Exception: ... : A component pin is used multiple times in a mapping error.
Each schematic symbol pin is used in only one mapping.
1. If you were to make two mappings with different component ports that each mapped to the same schematic symbol pin - this would elicit a Uncaught Exception: ... : A symbol pin is used multiple times in a symbol mapping. error.

Pin Properties Table¶

With the pin-properties table, we can simplify this mapping application by using the assign-symbol() command. With the pin-properties table, we can simplify this mapping application by using the assign-symbol() command.

pcb-component op-amp :

  pin-properties:
    [pin:Ref | pads:Int ...]
    [v-      | 1 ]
    [v+      | 2 ]
    [in+     | 3 ]
    [in-     | 4 ]
    [out     | 5 ]

  assign-symbol(op-amp-sym)


pcb-symbol op-amp-sym :
  pin v- at Point(0.0, -2.0)
  pin v+ at Point(0.0, 2.0)
  pin in+ at Point(-2.0, -1.0)
  pin in- at Point(-2.0, 1.0)
  pin out at Point(2.0, 0.0)

  ; More Symbol Geometry Here
  ...

In this example, we are leveraging the "Pin Properties" table to construct the port to symbol mapping automatically.

Notice how we haven't defined any port statements for this component. The pin-properties statement handles defining any missing ports.
Notice that the pin column in the table specifies ref symbols. These ref symbols must match with a pin in the pcb-symbol definition. This must be a 1:1 mapping.

Assuming that the ports that you want to define on the component match the pins on the pcb-symbol, this can be a convenient way to reduce duplication in the pcb-component definition.

Symbols are Internal to Components¶

The pcb-symbol assigned via the symbol statement is only used internally by the pcb-component definition. It is typically not possible nor useful for external entities to reference the symbol.

Further - there is no concept of "connecting" to a pcb-symbol. When constructing a circuit (net list) with the net statement, we can't connect to a pin of the pcb-symbol. We must connect to a port of the component.

Multi-part Symbols¶

It is often useful to create symbols that have multiple constituent parts. For example, a dual operational amplifier like the LM358LV contains two independent operational amplifiers. JITX provides multi-part symbol support via the unit statement.

Unit Statement Example¶

Complete design example for multi-part symbols

public defstruct OpAmpBank :
  in+:JITXObject
  in-:JITXObject
  out:JITXObject

public defn make-multi-opamp-symbol (banks:Seqable<OpAmpBank>, VCC:Pin, VEE:Pin) :
  inside pcb-component:
    symbol :
      val psym = ocdb/utils/symbols/power-supply-sym
      unit(0) = psym(VCC => psym.vs+, VEE => psym.vs-)
      for (bank in banks, i in 1 to false) do :
        val sym = ocdb/utils/symbols/multi-op-amp-sym
        unit(i) = sym(
          in+(bank) => sym.vi+,
          in-(bank) => sym.vi-,
          out(bank) => sym.vo
        )

Notice that the unit statement takes a single Int argument as the index into the multi-part symbol array. You can then assign any symbol with the = assignment operator.

; Example use `make-multi-opamp-symbol`
;
pcb-component DualOpAmp:
  port VCC
  port VEE

  port in1+
  port in1-
  port out1

  port in2+
  port in2-
  port out2

  ...
  val banks = [
    OpAmpBank(in1+, in1-, out1),
    OpAmpBank(in2+, in2-, out2)
  ]
  make-multi-opamp-symbol(banks, VCC, VEE)

When invoked, this results in a component with 3 parts: a sub-part symbol for the power rails and 2 sub-parts for the op-amp symbols.

Multi-part Symbol